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Permanent Magnet DC Motor

Publicado en: Ingeniería
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  1. 1. By Prof. Abhishek Gedam
  2. 2. In a dc motor, an armature rotates inside a magnetic field. Basic working principle of DC motor is based on the fact that whenever a current carrying conductor is placed inside a magnetic field, there will be mechanical force experienced by that conductor. Working Principle of DC Motor
  3. 3. Magnetic field is established by 1. Electromagnet 2. Permanent magnet.
  4. 4. permanent magnet dc motor or PMDC motor Permanent Magnet DC Motor
  5. 5.  stator is a steel cylinder  magnets are mounted in the inner periphery of this cylinder N – pole and S – pole of each magnet are alternatively faced towards armature Stator
  6. 6.  the steel cylindrical stator also serves as low reluctance return path for the magnetic flux.  Although field coil is not required in permanent magnet dc motor but still it is sometimes found that they are used along with permanent magnet. This is because if permanent magnets lose their strength, these lost magnetic strengths can be compensated by field excitation through these field coils. Stator
  7. 7. The rotor of pmdc motor is similar to other DC Motors. Consists of 1. Core 2. Windings 3. commutator Rotor
  8. 8.  Just similar to the general working principle of DC motor  the armature is placed inside the magnetic field of permanent magnet; the armature rotates in the direction of the generated force. Here each conductor of the armature experiences the mechanical force F = B.I.L Newton
  9. 9. PMDC Motor CDC Motor Voltage Equation V= 𝑰 𝒂 𝑹 𝒂 + 𝑬 𝒃
  10. 10. N α K Eb/Ø  By Armature voltage control  Field control is not possible As the magnetic field strength of a permanent magnet is fixed it cannot be controlled externally, field control of this type of dc motor cannot be possible
  11. 11. 1. No need of field excitation arrangement. 2. No input power in consumed for excitation which improve efficiency of dc motor. 3. No field coil hence space for field coil is saved which reduces the overall size of the motor. 4. Cheaper and economical for fractional kW rated applications.
  12. 12.  The magnetic strength of the field may get weak  There is also a chance of getting the poles permanently demagnetized (partial) due to excessive armature current during starting, reversal and overloading condition of the motor.  The field in the air gap is fixed and limited and it cannot be controlled externally. Therefore, very efficient speed control of DC motor in this type of motor is difficult.
  13. 13. Used where ?  small dc motors are required  very effective control is not required e.g. automobiles starter, toys, wipers, washers, hot blowers, air conditioners, computer disc drives